By forming a protective barrier, epidermal keratinocytes represent the first line of defense against environmental insults. UVB radiation of the sun is a major challenge for the skin and can induce ...inflammation, aging, and eventually skin cancer. UVB induces an immune response in human keratinocytes resulting in activation and secretion of the proinflammatory cytokines proIL-1β and -18. This is mediated by an assembly of protein complexes, termed inflammasomes. However, the mechanisms underlying sensing of UVB by keratinocytes, and particularly the types of inflammasomes required for cytokine secretion, are a matter of debate. To address these questions, we established a protocol that allows the generation of CRISPR/Cas9-targeted human primary keratinocytes. Our experiments showed an essential role of the NLRP1 rather than the NLRP3 inflammasome in UVB sensing and subsequent IL-1β and -18 secretion by keratinocytes. Moreover, NLRP1 but not NLRP3 was required for inflammasome activation in response to nigericin, a potassium ionophore and well-established NLRP3 activator in immune cells. Because the CRISPR/Cas9-targeted cells retained their full differentiation capacity, genome editing of human primary keratinocytes might be useful for numerous research and medical applications.
The Crosstalk between Nrf2 and Inflammasomes Hennig, Paulina; Garstkiewicz, Martha; Grossi, Serena ...
International journal of molecular sciences,
02/2018, Volume:
19, Issue:
2
Journal Article
Peer reviewed
Open access
The Nrf2 (nuclear factor E2-related factor or nuclear factor (erythroid-derived 2)-like 2) transcription factor is a key player in cytoprotection and activated in stress conditions caused by reactive ...oxygen species (ROS) or electrophiles. Inflammasomes represent central regulators of inflammation. Upon detection of various stress factors, assembly of the inflamasome protein complex results in activation and secretion of proinflammatory cytokines. In addition, inflammasome activation causes pyroptosis, a lytic form of cell death, which supports inflammation. There is growing evidence of a crosstalk between the Nrf2 and inflammasome pathways at different levels. For example, Nrf2 activating compounds inhibit inflammasomes and consequently inflammation. This review summarizes what is known about the complex and predominantly antagonistic relationship of both stress-activated pathways.
Nrf2 is a key regulator of the antioxidant defense system, and pharmacological Nrf2 activation is a promising strategy for cancer prevention and promotion of tissue repair. Here we show, however, ...that activation of Nrf2 in fibroblasts induces cellular senescence. Using a combination of transcriptomics, matrix proteomics, chromatin immunoprecipitation and bioinformatics we demonstrate that fibroblasts with activated Nrf2 deposit a senescence-promoting matrix, with plasminogen activator inhibitor-1 being a key inducer of the senescence program. In vivo, activation of Nrf2 in fibroblasts promoted re-epithelialization of skin wounds, but also skin tumorigenesis. The pro-tumorigenic activity is of general relevance, since Nrf2 activation in skin fibroblasts induced the expression of genes characteristic for cancer-associated fibroblasts from different mouse and human tumors. Therefore, activated Nrf2 qualifies as a marker of the cancer-associated fibroblast phenotype. These data highlight the bright and the dark sides of Nrf2 and the need for time-controlled activation of this transcription factor.
•Prolonged activation of Nrf2 promotes fibroblast senescence•Nrf2 controls expression and secretion of extracellular matrix components•Nrf2 activation induces a cancer-associated fibroblast phenotype•Senescent fibroblasts with activated Nrf2 promote wound closure but also tumorigenesis
Activation of the cytoprotective transcription factor Nrf2 is considered as a strategy for disease prevention. Hiebert et al. show that activating Nrf2 in fibroblasts promotes cellular senescence through production of a senescence-promoting matrisome, leading to accelerated wound closure but also increased tumor growth.
Inflammasome activation induces caspase-1–dependent secretion of the proinflammatory cytokine IL-1β. In addition, caspase-1 activates the protein GSDMD in immune cells, causing pyroptosis, a lytic ...type of cell death. In contrast, UVB irradiation of human primary keratinocytes induces NLRP1 inflammasome activation, cytokine secretion, and caspase-1–dependent apoptosis, rather than pyroptosis. Here, we addressed the molecular mechanisms underlying the role of caspase-1 in UVB-induced cell death of human primary keratinocytes. We show that GSDMD is a poor substrate of caspase-1 in human primary keratinocytes and that its activation upon UVB irradiation supports secretion of IL-1β. We screened for novel substrates of caspase-1 by a mass spectrometry–based approach and identified the specific cleavage of the major vault protein (MVP) at D441 by caspase-1 and -9. MVP is the main component of vaults, highly conserved ribonucleoprotein particles, whose functions are poorly understood. Cleavage of MVP is a common event occurring in human primary keratinocytes and fibroblasts undergoing apoptosis induced by different stimuli. In contrast, MVP cleavage could not be detected in pyroptotic cells. Cleavage of MVP by caspase-1 and -9 inactivates this cytoprotective protein. These results demonstrate a proapoptotic activity of caspase-1 and a crosstalk with caspase-9 upon inactivation of the cytoprotective MVP in apoptotic epithelial cells.
Caspase-1 has a crucial role in innate immunity as the protease activates the proinflammatory cytokine prointerleukin(IL)-1β. Furthermore, caspase-1 induces pyroptosis, a lytic form of cell death ...that supports inflammation. Activation of caspase-1 occurs in multi-protein complexes termed inflammasomes, which assemble upon sensing of stress signals. In the skin and in skin-derived keratinocytes, UVB irradiation induces inflammasome-dependent IL-1 secretion and sunburn. Here we present evidence that caspase-1 and caspase-4 are required for UVB-induced apoptosis. In UVB-irradiated human primary keratinocytes, apoptosis occurs significantly later than inflammasome activation but depends on caspase-1 activity. However, it proceeds independently of inflammasome activation. By a proteomics approach, we identified the antiapoptotic Bap31 as a putative caspase-1 substrate. Caspase-1-dependent apoptosis is possibly a recent process in evolution as it was not detected in mice. These results suggest a protective role of caspase-1 in keratinocytes during UVB-induced skin cancer development through the induction of apoptosis.
The transcription factor Nrf2 regulates the expression of genes required for protection from xenobiotic and oxidative stress. Under normal conditions Nrf2 is constantly degraded upon ubiquitination, ...mediated by the Nrf2 inhibitor Keap1. Inflammasomes represent stress‐induced protein complexes. They are critically involved in acute and chronic inflammation through caspase‐1‐mediated activation of pro‐inflammatory cytokines. Here, we demonstrate that Nrf2 is a positive regulator of the NLRP3 inflammasome. In contrast, Nrf2‐activating compounds, including the anti‐inflammatory drug dimethyl fumarate (DMF), inhibit inflammasome activation. Both effects are independent of the transcriptional activity of Nrf2 and, at least in part, not interdependent. On the other hand, NLRP3 inflammasome activation induces a rapid and partly caspase‐1‐ and Keap1‐independent degradation of Nrf2. These data argue against a simultaneous activation of both stress‐related pathways. Finally, we provide evidence that the cross‐regulation of both pathways is controlled by a physical interaction between the Nrf2/Keap1 and NLRP3 complexes.
The transcription factor Nrf2 is required for efficient NLRP3 inflammasome activation. This positive regulation might be mediated by a physical interaction between the Nrf2 and NLRP3 complexes. In contrast, Nrf2‐activating compounds, including the anti‐inflammatory drug DMF, inhibit inflammasome activation. Both effects are not dependent on Nrf2‐induced gene expression.
Inflammasomes are key intracellular signaling platforms involved in innate immune responses to micro-organisms and danger signals. Extracellular signal-regulated kinase, Jun N-terminal kinase, and ...p38 mitogen-activated protein kinase family members are activated by numerous environmental stresses. Recently, it has been reported that Jun N-terminal kinase is involved in inflammasome activation in myeloid immune cells. To date, the role of mitogen-activated protein kinase in inflammasome activity in keratinocytes has not been investigated. Here, we show that, in primary human keratinocytes, p38 mitogen−activated protein kinase is required for inflammasome activation and IL-1β secretion. Using selective small molecule inhibitors, small interfering RNA gene silencing, and CRISPR/Cas9-based deletion, we demonstrate the above and identify p38α and p38δ as critical regulators of ASC oligomerization, inflammasome activation, and IL-1β secretion in keratinocytes. Furthermore, our data suggest that the nature of the mitogen-activated protein kinase regulating inflammasome activity exhibits a certain cell specificity, with p38 playing a predominant role in keratinocytes and Jun N-terminal kinase 1 in cells of myeloid origin.
The pathological cascade leading from primary storage to neural cell dysfunction and death in metachromatic leukodystrophy (MLD) has been poorly elucidated in human-derived neural cell systems. In ...the present study, we have modeled the progression of pathological events during the differentiation of patient-specific iPSCs to neuroepithelial progenitor cells (iPSC-NPCs) and mature neurons, astrocytes, and oligodendrocytes at the morphological, molecular, and biochemical level. We showed significant sulfatide accumulation and altered sulfatide composition during the differentiation of MLD iPSC-NPCs into neuronal and glial cells. Changes in sulfatide levels and composition were accompanied by the expansion of the lysosomal compartment, oxidative stress, and apoptosis. The neuronal and glial differentiation capacity of MLD iPSC-NPCs was significantly impaired. We showed delayed appearance and/or reduced levels of oligodendroglial and astroglial markers as well as reduced number of neurons and disorganized neuronal network. Restoration of a functional Arylsulfatase A (ARSA) enzyme in MLD cells using lentiviral-mediated gene transfer normalized sulfatide levels and composition, globally rescuing the pathological phenotype. Our study points to MLD iPSC-derived neural progeny as a useful in vitro model to assess the impact of ARSA deficiency along NPC differentiation into neurons and glial cells. In addition, iPSC-derived neural cultures allowed testing the impact of ARSA reconstitution/overexpression on disease correction and, importantly, on the biology and functional features of human NPCs, with important therapeutic implications.
The Norrbottnian type of Gaucher disease (GD), as described many years ago, is due to a unique neuronopathic variant (c.1448T>G; L444P) that may have appeared during or before the sixteenth century ...in northern Sweden. It is a well-defined nosological entity with a characteristic course of clinical manifestations. In particular, Norrbottnian patients described in Sweden and Poland seem to share identical clinical histories characterized by the early onset of significant hepatosplenomegaly, often requiring splenectomy at an early age. Neurological involvement generally appears during the first or second decade of life, and includes horizontal gaze palsy, epilepsy, myoclonic movements, ataxia, dementia and cognitive impairment. Osteopenia occurs primarily in the spine, causing a severe and progressive thoracic kyphosis, although the involvement of other skeletal sites cannot be excluded. Here, we report on four Gaucher type 3 patients with Southern Italian ancestry presenting with clinical features and disease progression comparable to those of the 'Norrbottnian' Swedish phenotype, particularly regarding skeletal involvement with poor responsiveness to any therapeutical approach. Although a common ancestry among Southern Italian and Swedish Norrbottnian GD patients could not be investigated, the genotype L444P+L444P is the most frequently encountered in Southern Italy.
Inflammasomes comprise a group of protein complexes, which activate the protease caspase-1 upon sensing a variety of stress factors. Active caspase-1 in turn cleaves and thereby activates the ...pro-inflammatory cytokines prointerleukin (IL)-1β and -18, and induces unconventional protein secretion (UPS) of mature IL-1β, IL-18, as well as of many other proteins involved in and required for induction of inflammation. Human primary keratinocytes (HPKs) represent epithelial cells able to activate caspase-1 in an inflammasome-dependent manner upon irradiation with a physiological dose of ultraviolet B (UVB) light. Here, we describe the isolation of keratinocytes from human skin, their cultivation, and induction of caspase-1-dependent UPS upon UVB irradiation as well as its siRNA- and chemical-mediated inhibition. In contrast to inflammasome activation of professional immune cells, UVB-irradiated HPKs represent a robust and physiological cell culture system for the analysis of UPS induced by active caspase-1.
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